Electric cardiac pacemakers have proven effective in the long-term treatment of a large variety of heart dysfunctions, and accordingly, such devices constitute a preferred method of treating many of these afflictions. In general, pacemakers employ an electrode that is maintained in contact with the heart muscle, through which electrical stimulation of the heart muscle is achieved. Pacemakers commonly employ a flexible conductive lead that connects a remotely positioned power pack (usually implanted in a subcutaneous pocket beneath the pectoralis major or within the abdomen) to the electrode tip. The lead is typically routed through a vein leading to the heart so that the electrode is in contact with the heart muscle.
A particular problem associated with the implantation of such devices is the likelihood of dislodgement of the electrode tip from the heart wall occurring shortly after the implantation of the pacemaker. In an attempt to address this problem, active fixation means such as corkscrews or staples have been used to maintain the electrode tip in contact with the heart muscle. Alternatively, and preferably, passive fixation means have been employed to temporarily hold the electrode tip in contact with the heart muscle until sufficient tissue ingrowth has occurred about the electrode tip to hold it in place. Such a passive device is disclosed in Citron et al. U.S. Pat. No. 3,902,501, who provide a plurality of pliant tines extending from the electrode adjacent the tip and forming an acute angle with respect to the electrode body. The tines cooperate with the trabeculae in the heart muscle to hold the electrode tip in position until such time as natural fixation has occurred. However, because tines of the device of Citron et al. are angled acutely with respect to the electrode body, undue force is required to retract the lead once the tip has entered the heart chamber, as the tines must be folded back against the acute angle.
Accordingly, it is a principal object of the instant invention to provide a simplified passive fixation device for an electrode tip which does not hinder removal of the electrode from the heart chamber should that prove necessary.
It is a related object of the instant invention to provide a passive fixation device that assists in guiding the conductive lead of the pacemaker into a vein during implantation of the device.
These objects, and others which will become apparent upon reference to the accompanying drawings and following detailed description, are attained by a passive stabilizer that is secured to the lead of the cardiac stimulating device adjacent the electrode tip. The passive stabilizer comprises a sleeve having at least two groups of resilient tines, each group of tines being longitudinally displaced along the axis of the conductive lead with a first group being disposed between the second group and the electrode tip. The tines extend radially outwardly from the lead at a substantially right angle, with the tines of the first group extending outwardly a distance less than that of tines of the second group. Additionally, the tines of the first group are circumferentially staggered with respect to the tines of the second group.
Upon insertion of the conductive lead into a vein during the implantation of the pacemaker, the resilient tines fold back against the lead due to the constricting force of the vein. Because the tines of the two groups are circumferentially staggered, when the tines are forced to lay against the electrode lead during insertion, the tines of the one group will not interfere with the tines of the other group. After exiting from the vein into the desired heart chamber, the tines spring back to their original configuration in which the tines will interengage with the fibers in the heart muscle adjacent its wall to hold the electrode tip in place. In a preferred embodiment, there are four tines in each group, the tines in each group being circumferentially disposed from the adjacent tines in its group by approximately 90.degree.. The tines of one group are, in turn, circumferentially staggered at an interval of approximately 45.degree. with respect to the tines of the other group.